The commercial oven industry has never fully recovered from discovery that asbestos is extremely hazardous to human health and its subsequent banishment in 1985. Prior to that time, baking stones used as oven decks in commercial ovens were made from materials broadly described as transite. Transite is a hydraulically pressed cement-asbestos board and was mass produced from the 1940's until 1985. Since the production of transite was prohibited after the discovery of the harmful effects of asbestos, the commercial oven industry has yet to find an equivalent baking stone which provides the same baking qualities as transite despite the introduction of numerous asbestos-free baking stones.
The quality most desired in a baking stone is even or consistent thermal conductivity through the stone. If the stone conducts heat unevenly, the bottom portion of food resting on the stone will not cook evenly. For example, a pizza crust may be burned in some areas and actually undercooked in others. Of course, the baking stone must be resistant to cracking and delamination despite years of use at temperatures exceeding 500.degree. F.
Transite was manufactured from a combination of portland cement and asbestos fibers. Other manufacturers have searched for suitable fibers to combine with portland cement in order to achieve the desired baking qualities of transite. One such attempt is represented by the asbestos-free transite products. These products are manufactured from selected asbestos-free fibers and portland cement. The asbestos-free transite is not a satisfactory replacement for asbestos-containing transite because of surface cracking, delamination and uneven thermal conductivity through the asbestos-free transite stone.
Another product which was developed to replace transite is sold under the name promassal. Promassal is a mixture of calcium silicate hydrates, calcium silicate fillers, phyllosilicate fillers, natural organic fillers and residual quartz. However, promassal is characterized by the same inadequacies that characterize asbestos-free transite products. Namely, promassal baking stones are prone to surface cracking, delamination and uneven thermal conductivity through the stone. Specifically, promassal is not suitable for the higher temperatures used in baking pizza.
Currently, the material most commonly used for commercial oven baking stones is sold under the name cordierite. Cordierite is a magnesium-aluminum-silicate material. However, the cordierite stone is fragile and does not provide a consistent even cooking surface as required for hearth baked goods such as bread and pizza.
Thus, there is a need for a asbestos-free baking stone that would provide all of the benefits of the now discontinued asbestos-containing transite. This need has been felt since the abandonment of asbestos-containing products in the mid 1980's. The improvement contributed by the present invention solves the above illustrated problems and provides a baking stone that performs as well or better than the asbestos-containing transite. Further, the method of manufacture of the improved baking stone is a novel process in itself and enables the manufacturer to mass produce the improved baking stone.